FERMI-SURFACE AND HEAVY QUASI-PARTICLES OF URU2SI2

We present Shubnikov-de Haas measurements performed on two samples of URu2Si2 (I parallel to c end I parallel to a) in magnetic fields up to 24 T and at temperatures down to 60 mK. Four different energy bands c ould be determined between the [0 0 1]-[1 0 0] and the [1 0 0]-[1 1 0] directions of the tetragonal structure. Their corresponding cyclotron masses range between 5.8m(e) and 13.0m(e). The measured Fermi surface is compared to available band structure calculations. Surprisingly, f or magnetic fields oriented in the tetragonal plane, a nonlinear split ting of the 1.2 kT frequency could be discerned in the field range bet ween 17 and 21 T. (C) 1998 Elsevier Science B.V. All rights reserved.